"I'm having a great time," Joan Rivers crows before offering a brisk self-appraisal: "Everything is working, my mind is fine.

"The only time I play the age card is on planes when I'm trying to put a bag above the seat: 'I am 80 years old! Would someone PLEASE help me?!'"

Actually, she only turned 80 on Saturday, a milestone that has prompted the E! network to stage a Joan Rivers "takeover": Its regular one-hour edition of "Fashion Police" (airing Friday at 10 p.m. EDT) will be a black-tie birthday salute, preceded nightly through Thursday by special half-hours (at 10:30 p.m. EDT) featuring guest appearances by celebrities and even victims of past fashion slams.

This means frequent-flier Rivers would soon be back on a plane for Los Angeles to tape this five-day marathon while she marvels at the success of "Fashion Police," which, since premiering three years ago, has only tightened its grip in the culture as a wicked hybrid of style and snark.

Rivers is well-served by her co-hosts Giuliana Rancic, Kelly Osbourne and George Kotsiopoulos, all of whom can deliver shrewd analysis as well as piercing gibes at red-carpet infractions.

But "Fashion Police" is perfectly tailored to the comedic skills of Rivers as demonstrated by her 46-years-and-counting in show biz.

Hear her hail Uma Thurmond, sheathed in Versace at the Cannes Film Festival: "This gown is so feminine, so silver - it's the Anderson Cooper of dresses!"

"We do the jokes, and we tell the truth, too," Rivers sums up proudly. "E! told me, 'Whatever you want to say, you say.' We're having so much fun! And our lawyers are so dear."

Interviewed last week, she presides from an ottoman in the den of her vast Upper East Side Manhattan digs, a spread whose unabashed spectacle she dubs "Louis XIV meets Fred (Astaire) and Ginger (Rogers)."

It's 9 a.m. and Rivers, having apologized for being "only half-dressed," has presented herself in stocking feet and a chic, floor-length black-velvet caftan (part of her Joan Rivers Collection, she notes; she also has a jewelry collection).

She says her interest in fashion reaches back to her girlhood, when, still in school in New York, she had a job as a fashion coordinator at a department store chain, then another job where she assisted with the creation of Lord & Taylor's legendary Fifth Avenue window displays every Thursday night.

"If I hadn't gotten into show business," says Rivers, "I would have gone into fashion."

Not that any celeb should get her knickers in a twist over fashion feedback from any loose-lipped comedian - or so says Rivers, anyway.

"When you're making $20 million a picture and the dress is free, do you REALLY care if Joan Rivers says you shouldn't wear a peplum?" she chuckles. "I don't think Julia Roberts sits up at night thinking, 'She said WHAT?!''

To say what she has to say about couture catastrophes, Rivers is happy to hop a plane for the year-round weekly tapings of "Fashion Police" - just one piece of her on-the-go schedule that has seen no letup for decades and has its roots in her show-biz obsession as a child growing up in Brooklyn: She wanted to be an actress.

Only by chance did her definitive role become playing a comedian. Comedy was a way to pay the bills while she auditioned for dramatic parts.

"Somebody said, 'You can make six dollars standing up in a club,'" she explains, "and I said, 'Here I go!' It was better than typing all day."

In the early 1960s, comedy was a male-dominated game where the only women comics she could look to were Totie Fields and Phyllis Diller. But after several years of struggle, she landed a spot on "The Tonight Show" where host Johnny Carson gave her his blessing, saying she was destined to be a star.

A half-century later, Rivers' drive is undiminished. She never settles down.

The previous weekend she played three nights at Las Vegas' Venetian Resort.

She had then planned to go on to California. But she raced back East on a sad mission after getting a call. Barbara Waxler, her ailing older sister in Ardmore, Pa., had taken a turn for the worse. Flying into Philadelphia, Rivers reached her in her final hours.

"Aunt Joan is the head of the family now," says Rivers. "Look out! We're having pink flowers at the funeral!"

Rivers is no stranger to loss, including the suicide of her husband-producer-manager, Edgar Rosenberg, in 1987. Nor has her career, despite its towering heights, been immune to cruel setbacks, including her late-night talk show that launched the Fox network in 1986 but lasted less than a year.

"You never relax and say, 'Well, here I am!'" declares Rivers. "You always think, 'Is this gonna be OK?' I have never, in 46 years, taken anything for granted."

Except maybe the jokes she creates, tests and continuously fine-tunes. The jokes never stop. They can't.

"The trouble with me is, I make jokes too often," she says. "I'm making jokes at my sister's shivah. I was making jokes yesterday at the funeral home. That's how I get through life. Life is SO difficult - everybody's been through something! But you laugh at it, it becomes smaller."

Even the terror of aging - Rivers has always mocked it, not only with her self-directed jokes but also with her never-secret rounds of plastic surgery.

"But I have never wanted to be a day less than I am," she insists. "People say, 'I wish I were 30 again.' Nahhh! I'm very happy HERE. It's great. It gets better and better. And then, of course